The present invention relates to semiconductor fabrication and, more particularly, to an electrostatic chuck for use in, e.g., an etching apparatus and a method for manufacturing the electrostatic chuck.
In semiconductor manufacturing processes, etching processes, insulation film formation, and diffusion processes are repeatedly carried out. As is well known to those skilled in the art, there are two types of etching processes: wet etching and dry etching. Dry etching is typically implemented by using an inductively coupled plasma etching apparatus such as shown in FIG. 1. In the plasma etching apparatus shown in FIG. 1, reactant gas is led into chamber 11 via lead-in port 13. Semiconductor wafer W is held on chuck 12 in the chamber 11. High-frequency power is applied between chuck 12, which also serves as a lower electrode, and upper electrode 14 to generate plasma in chamber 11. Semiconductor wafer W itself or an insulation film or the like formed on the wafer is etched because of the chemical reaction caused by the radicals in the plasma or the accelerated ions.
In recent years, the use of electrostatic chucks has increased because these chucks exhibit excellent characteristics in a vacuum. Electrostatic chucks generate electrostatic absorbability between a sorbate and the chuck and thereby cause the chuck to absorb the sorbate. Electrostatic absorbability consists of two forces, namely, a coulombic force and a Johnsen-Rahbek force. FIG. 2 shows a monopolar type electrostatic chuck in which only positive electrode 22 is formed in dielectric material 21 and the apparatus and the plasma potential have a negative polarity. FIG. 3 shows a bipolar type electrostatic electrode in which two electrodes, namely, positive electrode 32 and negative electrode 33, are formed in dielectric material 31.
FIG. 4 shows an electrostatic chuck in which a ceramic layer is used as the dielectric material. As shown in FIG. 4, ceramic layer 53 is adhered on disk-shaped metal substrate 51 by an adhesive layer 52. High-melting point electrode 54 is embedded in ceramic layer 53. To increase the electrostatic absorbability, electrode 54 is embedded in ceramic layer 53 close to the surface thereof. Specifically, assuming that the thickness of ceramic layer 53 is, e.g., 1 mm, electrode 54 is embedded in the ceramic layer 53 at a position about 0.3 mm below the top surface of the ceramic layer and about 0.7 mm above the bottom surface of the ceramic layer. Further, circumferential cooling gas groove 55 is formed in the top surface of ceramic layer 53.
Helium gas is supplied to cooling gas groove 55 through a gas-supplying hole (not shown) that extends through ceramic layer 53 and metal substrate 51. Once the helium gas fills groove 55, the helium gas flows over the entire boundary surface between ceramic layer 53 and semiconductor wafer W. The flow of helium gas through the minute gap between ceramic layer 53 and semiconductor wafer W, which gap is created by the course surface of the ceramic layer, cools the semiconductor wafer. In dry etching, the temperature of semiconductor wafer W heavily influences the etching characteristics. By cooling semiconductor wafer W down to a temperature of about 30xc2x0 C. to about 60xc2x0 C. with helium cooling gas, the etching characteristics are improved.
However, in addition to alumina, the ceramic layer in a conventional electrostatic chuck includes impurities such as titanium oxide, chromic oxide, magnesia, and the like to provide the desired conductivity. These impurities are problematic because they may contaminate the backside of the semiconductor wafer. Another drawback of conventional electrostatic chucks is that the de-chucking responsibility deteriorates at lower temperatures because of the residual absorbability generated by the coulombic force.
In view of the foregoing, there is a need for an electrostatic chuck that minimizes contamination of the backside of the wafer and allows for smooth de-chucking of the wafer.
Broadly speaking, the present invention provides an electrostatic chuck having a high purity barrier layer. The present invention also provides a method for manufacturing the electrostatic chuck having the high purity barrier layer.
In accordance with one aspect of the present invention, an electrostatic chuck is provided. The electrostatic chuck includes a metal substrate. A conductive ceramic layer is disposed above the metal substrate. A high purity barrier layer is disposed above the conductive ceramic layer.
The thickness of the high purity barrier layer is preferably not more than about 200 xcexcm, and more preferably is in a range from about 20 xcexcm to about 100 xcexcm. The high purity barrier layer preferably has a purity of at least about 99%, and more preferably has a purity of at least about 99.99%. Exemplary materials from which the high purity barrier layer may be formed include alumina, silicon dioxide, silicon nitride, and sapphire.
In one embodiment, the conductive ceramic layer has an electric resistivity of not more than about 1012 xcexa9cm. In one embodiment, the high purity barrier layer has an electric resistivity of not less than about 1012 xcexa9cm. In one embodiment, the high purity barrier layer consists essentially of alumina having a purity of at least about 99.99%.
In accordance with another aspect of the present invention, a method for manufacturing an electrostatic chuck is provided. In this method, a metal substrate is provided. A ceramic layer is formed over the metal substrate. A high purity barrier layer is formed over the ceramic layer. In one embodiment, the high purity barrier layer is formed by plasma spray coating. Alternatively, the high purity barrier layer may be formed by chemical vapor deposition or sputtering.
The electrostatic chuck significantly reduces contamination of the backside of the semiconductor wafer and allows for smooth de-chucking of the wafer. When the high purity barrier layer of the present invention is used in a conventional Johnsen-Rahbek electrostatic chuck, a hybrid of the benefits of conventional Johnsen-Rahbek and coulombic electrostatic chucks is advantageously obtained in the thus-formed electrostatic chuck.
It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.